# Architecture Overview

A vertical-feature monorepo. Business capabilities are top-level packages; non-business foundations are `core-*`.

## Package map

```
packages/
  # Must-have foundation (no business logic)
  core-shared/    Generic primitives — Payload field/block helpers, tRPC init/context,
                  instrumentation interfaces, audit protocol + truncate-ip + AuditEntry shape,
                  BindContext + protocol types for optional cross-cutting cores
  core-cms/       Composition only: assembles feature CMS exports into one Payload config
  core-api/       Composition only: aggregates feature tRPC routers into one appRouter

  # Optional cross-cutting cores (scaffold on demand via `pnpm turbo gen core-package <name>`)
  core-trpc/      Frontend tRPC client + per-framework providers (Next.js, TanStack)
  core-ui/        Design-system primitives (atoms, molecules, generic organisms, templates)
  core-realtime/  Socket.IO server + broadcaster + handler registry (ADR-016)
  core-events/    In-memory + Payload-backed event bus + job queue (ADR-015)
  core-audit/     DPA-compliant audit logging — sinks, hook factories, eraseSubject (ADR-018)
  core-analytics/ Product analytics capture channel (ADR-024)
  core-consent/   Consent records + cookie-consent banner (ADR-025)
  core-dsr/       Data-subject-rights — export, delete, rectify, restrict (ADR-025)

  # Business capabilities
  auth/             Users + sign-in/sign-up/sign-out + session/cookie domain
  blog/             Articles collection + publishing flow
  media/            Media upload collection (skeleton; expand with optimization, CDN, etc.)
  marketing-pages/  Pages collection + SiteSettings global
  navigation/       Header global + menu items

  # Tooling
  core-eslint/     Shared ESLint flat config + conformance rules + boundary rules
  core-typescript/ Shared tsconfig + vitest base
  core-testing/    Factories, contract suites, recording test doubles
```

See `docs/architecture/template-tiers.md` for the must-have/optional split and the scaffold commands.

## Data flow

```
React component
  ↓ useQuery(trpc.blog.articleBySlug.queryOptions({slug}))      ← @repo/<feature>/ui (queries)
HTTP /api/trpc
  ↓
tRPC procedure (xProcedure.input(xInputSchema))               ← integrations/api/router.ts
  ↓ xProcedure has defineErrorMiddleware applied                ← integrations/api/procedures.ts
  ↓ container.get<IXController>(SYMBOL)
Controller factory (xInputSchema.safeParse)                   ← interface-adapters/controllers/<verb-noun>.controller.ts
  ↓ (useCase) => async (input: unknown) => Promise<view>
Use case factory                                              ← application/use-cases/<verb-noun>.use-case.ts
  ↓ (deps) => async (input: XInput) => XOutput
  ↓ ends with xOutputSchema.parse(result)
Repository implementation                                     ← infrastructure/repositories/<noun>.repository.ts
  ↓ getPayload({ config })
Payload Local API → Postgres
                                                              ↓ on throw:
                                            domain error → defineErrorMiddleware → TRPCError(code, cause)
                                                              ↓ on success:
                                            controller's `function presenter(value: XOutput)` shapes the view
                                                              ↓
                                                          tRPC response
```

Use cases and controllers are **factory functions** — they take their dependencies
as arguments and return the callable. The container wires them via
`.toDynamicValue((ctx) => factoryFn(ctx.container.get(...)))`. Each exports
`export type I*UseCase = ReturnType<typeof xUseCase>` (and the analogous
`I*Controller`) so consumers can depend on the type without importing the impl.
Controllers are **one per use case** — no multi-method controller files.

**Schemas live in the use-case file**: every use case exports
`xInputSchema` (a `z.ZodObject` with `.strict()`; `z.object({}).strict()` for
void inputs) and, for non-void use cases, `xOutputSchema`. Controllers and tRPC
procedures import the schema — never redefine it. The use case body validates
its output via `xOutputSchema.parse(...)` before returning, so a misbehaving
repository fails loudly at the layer that owns the contract.

**Controllers reshape via a co-located presenter**: every non-void
controller defines a top-level `function presenter(value: XOutput)` and returns
`Promise<ReturnType<typeof presenter>>`. Identity is fine — `return value;` —
but the function form is always present so adding a transform later is a
one-line edit. Void controllers (e.g. `signOutController`,
`deleteMediaController`) return `Promise<void>` and skip the presenter.

**Domain errors map to `TRPCError` per feature**: each feature owns
`integrations/api/procedures.ts` exporting `xProcedure = t.procedure.use(
defineErrorMiddleware([[Ctor, "TRPC_CODE"], ...]))`. Routers use `xProcedure`
instead of bare `publicProcedure`. `core-shared` provides the
`defineErrorMiddleware` factory but never enumerates a feature's errors —
each feature passes its own constructors in.

## Three enforcement layers

1. **`package.json` deps** — only declare allowed deps
2. **`exports` map** — each feature exposes a small public surface (`.`, `./ui`, `./cms`, `./api`, `./di/bind-production`, `./di/bind-dev-seed`)
3. **Two parallel automated checks**:
   - **ESLint `eslint-plugin-boundaries`** (lint-time) — enforces boundary rules at linting
   - **Turborepo `boundaries`** (build-graph time) — validates entire workspace dependency graph, including transitive reaches

Both use the same five-tag model; see "Five tags" section below.

## Five tags

The workspace is organized into five mutually exclusive tags:

- **app** (4 packages): `apps/cms`, `apps/web-next`, `apps/web-tanstack`, `apps/storybook`
- **core-composition** (2 must-have): `packages/core-api`, `packages/core-cms`. Plus `packages/core-trpc` when scaffolded via `pnpm turbo gen core-package trpc` (optional).
- **core** (1 must-have): `packages/core-shared`. Plus `core-ui`, `core-realtime`, `core-events`, `core-audit`, `core-analytics`, `core-consent`, `core-dsr` when scaffolded via `pnpm turbo gen core-package <name>` (optional).
- **feature** (5 packages): `packages/auth`, `packages/blog`, `packages/media`, `packages/marketing-pages`, `packages/navigation`
- **tooling** (3 packages): `packages/core-eslint`, `packages/core-typescript`, `packages/core-testing`

See `docs/architecture/template-tiers.md` for the must-have/optional split and the scaffold commands.

**Allowed dependency directions:**

| Tag              | May depend on                                 |
| ---------------- | --------------------------------------------- |
| app              | app, core, core-composition, feature, tooling |
| core-composition | core, core-composition, feature, tooling      |
| core             | core, core-composition, tooling               |
| feature          | core, feature, tooling                        |
| tooling          | tooling                                       |

A feature may import another feature's **public exports** — its `@repo/<feature>` contract barrel (types, errors, schemas, event contracts). It must not reach another feature's internals (the `exports` map seals those), and cross-feature _behaviour_ still flows through `IEventBus` — a feature never imports and invokes another feature's use cases directly.

**Composition exceptions:**

- `core-api` may import from `@repo/<feature>/api` subpath exports only
- `core-cms` may import from `@repo/<feature>/cms` subpath exports only
- `core-trpc` reaches features transitively through `core-api`'s `AppRouter` type

## Per-feature DI containers

Each feature owns its own InversifyJS `Container` + symbol table. No shared symbols, no cross-feature DI coupling. Tests rebind per feature without touching others. Apps call `bindProduction*(config)` per feature at boot to swap the default mock implementations for Payload-backed ones.

## Spec reference

`docs/architecture/vertical-feature-spec.md` is the canonical design.

## Interactive explainers

Four single-file HTML walkthroughs sit alongside this overview. They're self-contained (no build step) and best viewed locally in a browser.

- [`data-flow-explainer.html`](./data-flow-explainer.html) — request and event flow through one feature, with the DI binding mode toggle and feature swap controls.
- [`di-explainer.html`](./di-explainer.html) — the full container + symbols + binder lifecycle.
- [`feature-conformance-explainer.html`](./feature-conformance-explainer.html) — companion to ADR-020-adjacent conformance design (also linked from `agent-first-workflow-and-conformance.md` and `runbook.md`).
- [`audit-and-compliance-explainer.html`](./audit-and-compliance-explainer.html) — companion to ADR-018 (also linked from `dependency-flow.md` and `guides/audit-and-compliance.md`).

The four pages cross-link to each other; entering any of them surfaces the others.
